Mapping peripheral refraction over a 90° field of view (FOV) using a modified widefield fundus camera

Abstract

Purpose : Measurement of peripheral refraction has the potential for predicting development of myopia. The detection of retinal shape abnormalities associated with disease could also provide other information such as swelling caused by wet AMD, or retinal distortion associated with posterior staphyloma.

Methods : The CLARUS^TM 500 fundus camera (ZEISS, Dublin, CA) uses slit-scanning technology to illuminate the retina with horizontal strips of light entering at the top and bottom of the pupil, providing the potential for measuring eye shape. By measuring the relative vertical shift on the retina between the upper and lower illuminations using prototype software, we were able to map the vertical refraction across the full field of view of the imager. As this measurement is affected by the field curvature inherent in the optical design, we model this curvature as a function of camera focus and remove it from the measurement. To demonstrate the accuracy and repeatability of the mapping, we created a spherical test eye with rings alternating between 9.5 and 10 diopters of hyperopia, and measured it with focal settings of the camera ranging from 0 to 11 diopters. We then measured human eyes, generating both the peripheral refraction maps and corresponding fundus images.

Results : The horizontal meridian from the test eye peripheral refraction map with the fundus camera set to 10 diopters is shown in Figure a). As can be seen in the plot, the refraction oscillates between roughly 9.5 and 10 diopters as expected. Figure b) shows the peripheral refraction map from a 1D hyperopic human subject, with the corresponding fundus image in Figure c). The fundus image was generated using the peripheral refraction data so as to ensure co-alignment.

Conclusions : The slit-scanning fundus camera technology can be used for mapping peripheral refraction. This has potential applications for both myopia research and clinical diagnosis, and for evaluation of any other diseases that might affect retinal shape.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Figure a) Horizontal meridian from the test eye peripheral refraction map with the fundus camera set to 10 diopters. Figure b) Peripheral refraction map from a 1D hyperopic human subject. Figure c) Corresponding fundus image. The central region is not measured because of interference from reflections from the optics.